This nonprovisional application claims priority under 35 U.S.C. xc2xa7119(a) on Patent Application No. 2001-328861 filed in Japan on Oct. 26, 2001, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a trisazo compound useful as a coloring matter for an aqueous ink for writing materials or for an aqueous ink for ink jet recording.
2. Description of the Related Art
In the field of ink jet printing, there is a constant demand for high-speed and highly accurate printing. The level of the demand are becoming higher and higher. For example, high fastness such as light resistance and water resistance of printed materials, long-term stability of ink performance, safety and high-quality printing on various types of paper typified by plane paper and the like have recently been required. While the qualities that printed materials are required are becoming higher, the conventional dyes used as coloring matters of inks are unsatisfactory in density of printed materials and fastness with respect to water resistance and light resistance thereof, and are poor in long-term stability of ink. Thus, the conventional dyes have been becoming very difficult to simultaneously satisfy the many required qualities.
Under these circumstances, there are many attempts to satisfy the demands for density, water resistance and light resistance of printed materials by using pigments as coloring matters of printing inks. However, pigments have still not reached the levels of the dyes in print qualities and have problems with respect to long-term stability with time as ink. Therefore, pigments have not satisfied the demands sufficiently.
Further, pigments result in high cost because they require highly developed manufacturing techniques for the improvement in their physical and chemical properties such as dispersibility, stability with time and print density; pigments have disadvantage for providing low-cost products. Therefore, in the field of ink for ink jet, there is a particularly strong demand for dyes excellent in fastness with respect to density, water resistance and light resistance of printed materials.
In Japanese Patent Laid-Open Publication No. 2000-309721, a dye shown below is proposed that yields a recorded image of high density and of high toughness when printing is conducted on plain paper and that provides an ink stable for a long term. 
wherein X represents a carboxyl group, a sulfo group or a hydrogen atom, l and m each independently represent 0 or 1 and satisfy l+m=1, q represents 0 or 1, Z represents a hydrogen atom or a phenyl group that may be substituted with a carboxyl group or a sulfo group, provided that when q is 0, Z represents a phenyl group that may be substituted with a carboxyl group or a sulfo group.
The dyes disclosed in this publication show improvements in print density, light resistance and the like achieved by complicating functional groups of disazo dyes disclosed in Japanese Patent Laid-Open Publication No. H5(1993)-262998, etc. However, it is difficult for general synthetic methods by using xcex3 acid (2-amino-8-naphthol-6-sulfonic acid) as a final coupling component to provide high purity.
The reason for this is that a derivative of xcex3 acid intrinsically has a plurality of sites where the coupling reaction may take place (Chemistry of Synthetic Dyes, p. 154, published by Maki Shoten Co., Ltd.) and therefore, a single compound cannot be produced experimentally under alkaline condition through coupling with a diazonium salt made from a monoazo compound.
A dye generally contains a great large variety of impurities other than its main component and it is often difficult to analyze each of the impurity and to investigate its interaction with other components. However, as the amounts of the impurities increase, the probability that they interact mutually increases. The increase in the probability will appear as a degree of degradation, that is, as deterioration in storage stability or toughness such as light resistance when it is formulated into an ink.
There are few dyes that have a structure similar to that of the trisazo compound of the present invention. For example, the dyes having structure of H acid (1-amino-8-naphthol-3,6-disulfonic acid) are known widely. Examples of the known compounds include Naphthol Blue Black of the structure shown below. 
However, when an ink for ink jet recording is prepared by using only this disazo dye, optical density of the recorded image becomes insufficient, hue thereof also becomes unsatisfactory as a black ink, and its light resistance nor water resistance is not in the level for actual use. Further, the ink has a problem in dissolution stability of the dye.
In Japanese Patent Examined Publication No. S61(1986)-18590, a tetrakisazo dye of the structure shown below is used in a recording medium solution. However, it is, in general, difficult to obtain this kind of tetrakisazo dye as a high-purity product. 
The objective of the present invention is to provide a high-purity trisazo compound with excellent light resistance that is useful as a coloring matter for a black aqueous ink for ink jet recording and the like.
Thus, the present invention provides a trisazo compound represented by the formula: 
wherein A1 is a group represented by the formula xe2x80x94COOM or xe2x80x94SO3M wherein M is each independently a hydrogen atom, ammonium, alkali metal, hydroxyammonium, alkylammonium or alkanolammonium, A2 is a hydrogen atom or a group represented by the formula xe2x80x94COOM or xe2x80x94SO3M wherein M is the same as that described above, R is each independently a hydrogen atom, an alkyl group having from 1 to 6 carbon atoms, an alkoxy group having from 1 to 6 carbon atoms, a hydroxyl group, a sulfamoyl group, a carbamoyl group, a cyano group, an acetyl group, a sulfonic acid group, a carboxyl group or a halogen atom, B is a moiety represented by the formula: 
wherein, M is the same as that described above, Nps is a moiety represented by the formula: 
wherein M is the same as that described above; or the formula: 
wherein M, A1, R, B and Nps are the same as those described above.
Further, the present invention also provides a water-soluble dye containing the above-mentioned trisazo compound in an amount of not less than 85% by weight.
The water-soluble trisazo compound of the present invention has high purity. When the compound is used as a dye for an aqueous black ink for ink jet recording or the like, the ink has good dissolution stability and provides recorded images excellent in print density, light resistance and water resistance.